Prosthetic implant and method of implantation

ABSTRACT

A prosthetic implant useful in a cementless application is disclosed. The implant may include a curved bone facing surface and one or more pegs or keels. Preferably, the implant is implanted on a bone surface that has been prepared so as to allow for a snap fit between the implant and the bone.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of the filing date of U.S.Provisional Patent Application No. 61/500,257 filed Jun. 23, 2011, thedisclosure of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

In a traditional knee arthroplasty surgery, the diseased bone and/orcartilage of a patient is removed and replaced with a prostheticimplant. A surgeon typically prepares the bone using a hand-heldoscillating saw blade or other cutting instrument guided by a resectionguide or the like, which results in a series of planar bone surfaceresections. Additionally, the surgeon may use a drill, broach, tamp orother instrument to make holes, slots, depressions or the like in thebone. The planar bone resections and cylindrical bone holes are orientedto interface with flat surfaces and pegs and/or keels formed on a boneengaging surface of a prosthetic implant. An opposite side of theimplant includes an articulation surface that is preferably designed toarticulate with a like articulation surface formed on an implant to beimplanted on the other bone of the knee.

Although implants designed to be implanted on planar cut surfaces ofbones have been more widely utilized, implants meant to be implanted onnon-planar surfaces have been designed and utilized in surgicalprocedures. The preparation methods for such implants are often verydifferent than for the above-discussed traditional implants. Forinstance, milling devices are often utilized to prepare the bone surfaceto receive the implant. Again, these implants may employ pegs and/orkeels to aid in the fixation of implant to the bone. Additionally, likein the traditional planar cut implants, cement or another fixationcompound may be utilized to guarantee a solid connection between theimplants and the bone.

One drawback in utilizing cements or the like is that the requiredcement layer often results in an unwanted transformation from a veryprecisely prepared surface to an imprecise prepared bone surface. Thisis largely due to the imprecise nature of working with cement. In asituation where a bone surface has been prepared to meet very specificdimensions, application of cement prior to implanting the implant willresult in the surface exhibiting less than precise dimensions.

Therefore, there exists a need for implants that do not require the useof cement or the like, but yet remain attached to the bone afterimplantation.

BRIEF SUMMARY OF THE INVENTION

A first aspect of the present invention is a prosthetic implantincluding a first end, a second end, an articular surface, a bonecontacting surface including a curved portion, a first element extendingfrom the bone contacting surface and having a first curved surface and asecond element extending from the bone contacting surface and having asecond curved surface. The first and second curved surfaces arepreferably curved about a first pivot point.

In other embodiments of this first aspect, the implant may furtherinclude a third element extending from the bone contacting surface andhaving a third curved surface, where the third curved surface is alsocurved about the first pivot point. The first and second curved surfacesmay face the first end and the pivot point may be adjacent the firstend. The implant may also include a third element extending from thebone contacting surface, the third element being located adjacent thesecond end. The third element may be at least partially arcuate.

In still further embodiments of the first aspect of the invention, thefirst element may further include a third curved surface and the secondelement further include a fourth curved surface, the third and fourthcurved surfaces being curved about the first pivot point. The bonecontacting surface may also include a flat portion defining a firstplane, the first pivot point located along the first plane. In thisconstruction, the first pivot point may be spaced apart from the firstend. In another embodiment, the bone contacting surface may include aflat portion defining a first plane, the first pivot point located apartfrom the first plane. Again, the first pivot point may be spaced apartfrom the first end. In certain embodiment, the implant may be a femoralcomponent, a tibial component, a patello-femoral component, or the like.

Another aspect of the present invention is another prosthetic implantincluding a first end, a second end, an articular surface, a bonecontacting surface including a curved portion, a first element extendingfrom the bone contacting surface and having a first curved surface and asecond element extending from the bone contacting surface and having asecond curved surface. The first curved surface may be curved about afirst pivot point and the second curved surface may be curved about asecond pivot point.

In another embodiment according to the second aspect, the implantincludes a third element extending from the bone contacting surface andhaving a third curved surface, where the third curved surface is curvedabout one of the first or second pivot points. The first and secondcurved surfaces may face the first end and the first and second pivotpoints may be adjacent the first end. The implant may further include athird element extending from the bone contacting surface, the thirdelement located adjacent the second end. The third element may be atleast partially arcuate.

In other embodiments, the first element may further include a thirdcurved surface and the second element may further include a fourthcurved surface, the third curved surface being curved about the firstpivot point and the fourth curved surface being curved about the secondpivot point. The bone contacting surface may include a flat portiondefining a first plane, the first and second pivot points located alongthe first plane. The first and second pivot points may be spaced apartfrom the first end. In other embodiments, the bone contacting surfacemay include a flat portion defining a first plane, the first and secondpivot points located apart from the first plane. The first and secondpivot points may be spaced apart from the first end. In the variousembodiments, the implant may be a femoral component, a tibial component,a patello-femoral component or the like.

Yet another aspect of the present invention is a method of arthroplastyincluding the steps of creating a first resected bone surface on a firstend of a bone, at least a portion of the first resected bone surfacebeing non-planar, preparing a first cavity extending into the firstresected bone surface, providing a prosthetic implant, the implantincluding an articular surface, a bone contacting surface including acurved portion and a first element extending from the bone contactingsurface and having a first curved surface, the first curved surfacecurved about a first pivot point and coupling the implant by pivotingthe implant about the first pivot point until the first element becomesdisposed within the first cavity.

In an embodiment according to this aspect, the making step may includeutilizing any suitable cutting instrument including, but not limited to,a miller, handheld cutting implement or a cutting tool coupled with arobot. The preparing step may further include preparing a second cavityextending into the first resected bone surface. The implant may includea second element extending from the bone contacting surface and having asecond curved surface, the second curved surface curved about the firstpivot point, and the implanting step may include disposing the secondcurved surface within the second cavity. Additionally, the implant mayinclude a second element extending from the bone contacting surface andhaving a second curved surface, the second curved surface curved about asecond pivot point, and the implanting step may include disposing thesecond curved surface within the second cavity. The first and secondpivot points are at different locations.

In other embodiments, the first element may include a second curvedsurface. The preparing step may include preparing the first cavity toinclude a third curved surface corresponding to the first curved surfaceand a fourth curved surface corresponding to the second curved surface.The first, second, third and fourth surfaces may be curved about thefirst pivot point. The first and second surface may be curved about thefirst pivot point and the third and fourth surfaces may be curved abouta second pivot point, the first and second pivot points being atdifferent locations. The implant may further include a first projectionfacing a first end of the implant.

In still further embodiments, the method may further include the step ofcreating a first divot in the first resected surface. The implantingstep may include disposing the first projection within the first divot.The method may further include the step of creating a second divot andthe implanting step may further include disposing the first projectionwithin the second divot. The first projection may be ball shaped,cylindrical or the like. The bone contacting surface may include a flatportion defining a first plane, the first pivot point located along thefirst plane or located apart from the first plane. The implanting stepmay be performed through the use of a robot or other suitable means.

Another aspect of the present invention is a prosthetic implantincluding an articular surface and a bone contacting surface. A firstelement extending from the bone contacting surface has a first centerand a first radius. A second element extending from the bone contactingsurface has a second radius and a third radius. The first radius, thesecond radius and the third radius are concentric about the firstcenter.

In one embodiment of this aspect, the prosthetic implant may furthercomprise a third element that extends from the bone contacting surfaceand has a fourth radius. The fourth radius being concentric about thefirst center.

Another aspect of the present invention is a method of bone preparationand insertion of a unicondylar prosthetic implant. The method mayinclude utilizing any suitable cutting instrument including, but notlimited to, a miller, handheld cutting implement or a cutting instrumentcoupled to a robot or the like to make a non-planar resection on adistal femoral bone and using the robot/cutting instrument construct toprepare a first cavity and a second cavity extending into the bone. Themethod further includes implanting a unicondylar implant by following animplantation path having a first center that follows an approach pathuntil a first element thereof contacts the first cavity, and thenfollows a substantially curved path until the first element is fullyseated in the first cavity and a second element is fully seated in thesecond cavity.

In one embodiment of this aspect, the unicondylar implant may beimplanted through the use of a robot or the like.

In another embodiment of this aspect, the second cavity has an anterioraspect and a posterior aspect, and the second element further includesan anterior surface and a posterior surface, wherein the anteriorsurface has an interference fit with the anterior aspect of the secondcavity and at least a portion of the posterior surface has a clearancefit with the posterior aspect of the second cavity.

Another aspect of the present invention is a system for surgery. Thesystem includes a prosthetic implant having an articular surface and afirst element, the first element having a first center. The system mayfurther include any suitable cutting instrument including, but notlimited to, a miller, handheld cutting implement or a bone preparationsystem coupled with a robot or the like for preparing a non-planargeometry and a robot or the like for inserting the prosthetic implantinto the non-planar geometry. The system may further include animplantation path programmed into the robotic, wherein the first centeris coincident along the implantation path during implantation.

In one embodiment of this aspect, the implantation path follows a firstlinear path until the first element contacts the bone, and then followsa second curved path until the prosthetic implant is fully seated intothe prepared bone.

In another embodiment of this aspect, the prosthetic implant has asecond element which has a first surface having a geometry that isconcentric about the first center.

In yet another embodiment of this aspect, the prosthetic implant rotatesabout the first center while the first center remains coincident aboutthe implantation path while moving along the implantation path. Theconcentric geometries form a concentric path about the first centerduring rotation.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood on reading the followingdetailed description of non-limiting embodiments thereof, and onexamining the accompanying drawings, in which:

FIG. 1 is a perspective view of an implanted three part implant systemaccording to one embodiment of the present invention.

FIG. 2 is another perspective view of the implanted three part implantshown in FIG. 1.

FIG. 3 is yet another perspective view of the implanted three partimplant shown in FIG. 1.

FIG. 4 is an exploded view of the three part implant shown in FIG. 1.

FIG. 5 is a perspective view of a femoral condyle implant of the threepart implant shown in FIG. 1.

FIG. 6 is a side view of the femoral condyle implant shown in FIG. 5.

FIG. 7 is a cross sectional view the taken along line A-A of FIG. 6.

FIG. 8 is an enlarged view of area A of FIG. 7.

FIG. 9 is a partial cross sectional view of the implant of FIG. 5 andits relationship with a prepared tibia.

FIGS. 10A-10C are partial cross sectional view of the implant of FIG. 5being implanted on a prepared femur.

FIG. 11 is an enlarged cross sectional view depicting the relationshipshown in FIG. 9.

FIG. 12-14 are enlarged views focusing on a portion of the relationshipshown in FIG. 11.

FIGS. 15-16 are enlarged views similar to those of FIGS. 12-14 depictingan alternately prepared bone.

FIG. 17 is a partial cross sectional view similar to FIG. 9 depicting analternately prepared bone.

FIG. 18 is an enlarged cross sectional view similar to FIG. 11 depictingthe alternate bone preparation shown in FIG. 17.

FIGS. 19 and 20 are partial cross sectional views similar to FIGS.10A-10C depicting the alternate bone preparation shown in FIG. 17.

FIG. 21 is a perspective view of implanted tibial implants in accordancewith the present invention.

FIG. 22 is an explode view of the tibial implants shown in FIG. 21.

FIG. 23 is a perspective view of the lateral tibial implant shown inFIG. 21.

FIG. 24 is a bottom view of the lateral tibial implant shown in FIG. 21.

FIG. 25 is another perspective view of the lateral tibial implant shownin FIG. 21.

FIG. 26 is a front view of the lateral tibial implant shown in FIG. 25.

FIG. 27 is a side view of the lateral tibial implant shown in FIG. 25.

FIG. 28 is a side view of the lateral tibial implant shown in FIG. 21depicting the relationship of certain of its components.

FIG. 29 is a side view of another embodiment lateral tibial implantsimilar to that shown in FIG. 21 depicting the relationship amongcertain of its components.

FIG. 30 is a perspective view of a bi-cruciate retaining (“BCR”) tibialimplant according to another embodiment of the present invention.

FIG. 31 is a top view of the BCR implant shown in FIG. 30.

FIG. 32 is a side view of the BCR implant shown in FIG. 30 depicting therelationship among certain of its components.

FIG. 33 is a perspective view of a BCR implant according to anotherembodiment of the present invention.

FIG. 34 is a side view of the BCR implant shown in FIG. 33.

FIG. 35 is a front view of the BCR implant shown in FIG. 33.

FIG. 36 is a side view of the BCR implant shown in FIG. 33 depicting therelationship among certain of its components.

FIG. 37 is a perspective view of a patello-femoral implant according toanother embodiment of the present invention.

FIG. 38 is an alternate perspective view of the implant shown in FIG.37.

FIG. 39 is a side view of the implant shown in FIG. 37.

FIGS. 40a-40d are a series of cross-sectional views illustrating amethod of implantation for the implant shown in FIG. 37.

FIG. 41 is a perspective view of another embodiment a patello-femoralimplant of the present invention.

FIG. 42 is a side view of the implant shown in FIG. 41.

FIG. 43 is a perspective view of one embodiment of a distal femoral bonewith a unicondylar implant of the present invention.

FIG. 44 is a perspective view of the unicondylar implant shown in FIG.43.

FIG. 45 is a side view of the implant shown in FIG. 43.

FIGS. 46a-46c are a series of cross-sectional views illustrating amethod of implantation for the implant shown in FIG. 43.

FIG. 47 is a perspective view of another embodiment of a unicondylarimplant of the present invention.

FIG. 48 is a side view of the implant shown in FIG. 47.

FIG. 49 is a perspective view of another embodiment of a unicondylarimplant according to the present invention.

FIG. 50 is a side view of the implant shown in FIG. 49.

FIG. 51 is a partial cross sectional view of the implant of FIG. 49implanted on a femur.

FIG. 52 is another partial cross sectional view of the implant of FIG.49 implanted on a femur.

FIG. 53 a perspective view of another embodiment of a unicondylarimplant according to the present invention.

FIG. 54 is a side view of the implant shown in FIG. 53.

FIG. 55 is a partial cross sectional view of the implant of FIG. 53implanted on a femur.

FIG. 56 is another partial cross sectional view of the implant of FIG.54 implanted on a femur.

FIG. 57 is a perspective view of another embodiment unicondylar implantaccording to the present invention.

FIG. 58 is a side view of the unicondylar implant shown in FIG. 57.

FIG. 59 is a partial cross sectional view of the implant of FIG. 57implanted on a femur.

FIG. 60 is a top view of a tibial implant and associated interfacewithin a proximal tibial bone according to another embodiment of thepresent invention.

FIG. 61 is a perspective view of the implant and tibial bone of FIG. 60.

FIG. 62 is a cross sectional view of the implant and tibial bone of FIG.60.

FIG. 63 is an enlarged cross sectional view of the implant and tibialbone of FIG. 60.

FIG. 64 is a cross-sectional view of the tibial implant shown in FIG. 60further compromising geometric relationships between the implant and thebone.

FIGS. 65-67 are different perspective views illustrating yet anotherpatello-femoral implant according to another embodiment of the presentinvention.

DETAILED DESCRIPTION

As used herein, the term “distal” means more distant from the heart andthe term “proximal” means closest to the heart. The term “inferior”means toward the feet and the term “superior” means towards the head.The term “anterior” means towards the front part of the body or the faceand the term “posterior” means towards the back of the body. The term“medial” means toward the midline of the body and the term “lateral”means away from the midline of the body.

The present invention addresses the aforementioned shortcomings withcertain of the prior art implants. Specifically, the present inventionprovides implants that can be implanted with or without the use ofcement or other adhesive, but remain attached to the bone even ininstances where no cement or other adhesive is utilized. Althoughdiscussed below primarily in connection with knee arthroplastyprocedures, it should be noted that implants according to the presentinvention can be modified for use in other joints throughout the body.For instance, while the main aim of the implants shown and described inthe present application relate to implants for the distal femoralsurface and the proximal tibial surface, implants according to thepresent invention could be utilized in the shoulder, spine, hip, patellaor the like. In addition, although the present implants are designed tobe implanted without the use of cement or the like, it should beunderstood that such compounds could be utilized to further ensureproper attachment of the implants to the bone.

Turning now to the various embodiments of the present invention, FIGS.1-4 depict a three-part implant system including a patello-femoralimplant 10, a medial femoral condyle implant 12, and a lateral femoralcondyle implant 14. As is apparent from the exploded view of FIG. 4,those three implants are designed for implantation both within recessesand on flat cuts formed in the distal end of the femur. This type ofdesign will be referred to herein as an inlay/onlay construction. Forinstance, patello-femoral implant 10 is implanted in a patello-femoralrecess 16 and on a patella-femoral flat 17, medial femoral condyleimplant 12 is implanted in a medial condyle recess 18, and lateralcondyle implant 14 is implanted in a lateral condyle recess 20. Recesses18 and 20 may in fact include portions that when viewed from a specificorientation appear flat. For instance, FIGS. 9-10C depict a posteriorportion of one of the recessed that appears flat in the particular viewsshown. However, it is to be understood that, when viewed from differentorientations (e.g., from an orientation rotated ninety degrees from thatshown in FIGS. 9-10C), those “flat” portions may in fact exhibit acurvature. Moreover, it is to be understood that recesses 18 and 20 mayinclude portions that are surrounded by unresected (e.g., on theanterior end of the condyles) and other portions that are not surrounded(e.g., on the posterior end of the condyles). As is best shown in FIG.1, the cooperation of the implants and the prepared bone creates anarticulation surface on the distal end of the femur that consists ofboth the implants and the natural femoral cartilage (i.e., the cartilageextending between the prepared surfaces). Of course, implants 10, 12, 14may be designed to cooperate with a distal end of the femur that iscompletely prepared, not just prepared within the aforementionedrecesses.

Turning now to FIGS. 5-8, the general design of certain of the commonfeatures between femoral condyle implants 12 and 14 will be described.It should be noted that in certain embodiments, the construction ofthese common features of femoral condyle implants 12 and 14 aresubstantially similar, but may vary in other embodiments. Moreover,other aspects of femoral condyle implants 12 and 14 may varysignificantly in order to ensure the cooperation of the particularimplant with the different anatomical features of the lateral and medialfemoral condyles. As shown, both implants 12 and 14 include anarticulation surface 22 and a bone engaging surface 24. Articulationsurface 22 may be of any shape designed to cooperate with acorresponding articulation surface formed on a tibial implant, such asthe tibial implants discussed below. In this regard, it should beunderstood that articulation surface 22 may vary greatly depending uponthe overall construction of the other components of the system. Forinstance, the articulation surfaces described in U.S. Pat. Nos.7,160,330 and 7,628,817, the disclosures of which are herebyincorporated by reference herein, may be employed in the implantdesigns. Bone engaging surface 24 is generally curvate, although it maybe only partially curvate in other embodiments, with three componentsextending therefrom, a first peg 26, a second peg 28, and a snap feature30. It should be understood that although specific structures such aspegs 26 and 28 and snap feature 30 are depicted in the drawings anddescribed herein, other structures are indeed contemplated, includingthe use of keels, spikes and the like. With respect to its curvature,bone engaging surface 24 is curved both in an anterior to posteriordirection (see FIGS. 5 and 6) and in a medial to lateral directiondenoted by curvature 32 (see FIGS. 7 and 8). Moreover, surface 24includes lateral and medial flat run outs 34 and 36 (best shown in FIGS.7 and 8). In essence, run outs 34 and 36 allow for a smooth transitionbetween the implant and the bone surrounding the recesses into which theimplants are placed, while ensuring implant stability. In a similarfashion to the above-discussed recessed which are formed in the bone,run outs 34 and 36 are preferably only flat when viewed from theparticular orientation depicted in FIGS. 7 and 8. However, when viewedfrom an orthogonal orientation, the run outs may in fact be curved. Inthe particular configuration shown, the orientation of the flat run outsis substantially perpendicular to the planned loading direction of theimplant to ensure maximum stability. In addition, the run outs serve asa termination of the bone contacting surface, which in turn, determinesthe amount of bone that needs to be prepared for accepting the implant.

As best shown in FIG. 9, first and second pegs 26, 28 are situated in amanner that facilitates a snap, press or interference fit with the bone.It should be recognized that these fits may be facilitated in variousways, including through line-to-line cooperation between and among thevarious implant components (e.g., pegs 26, 28) and the prepared bone.Moreover, as will be discussed more fully below, the particularorientation of the implant components and/or the prepared surfaces ofthe bone may create the given fit. More specifically, first peg 26includes an anteriorly facing surface at least a portion of which iscurved along a first imaginary circle 38, and a posterior facing surfaceat least a portion of which is curved along a second imaginary circle40. Likewise, an anterior facing surface of second peg 28 is curvedalong a third imaginary circle 42, and a posterior facing surface ofthat peg is curved about a fourth imaginary circle 44. As is depicted inFIG. 9, each of those four circles is centered about a center point 46,which in the embodiment disclosed in FIG. 9 serves as a pivot point forthe implant (as will be discussed more fully below). Center/pivot point46 happens to be adjacent an anterior surface of the implant in theembodiment shown, however, it should be understood that such point couldbe located away from the implant or at various location on the implant.

In a preferred method of implanting the embodiment implant shown, thedistal end of the femur is prepared so as to include an overall profilecomplementary to that of bone facing surface 24 and first and secondholes 48 and 50 for receiving pegs 26 and 28, respectively. Hole 48includes a posteriorly facing surface at least a portion of which iscurved along circle 38 and an anteriorly facing surface at least aportion of which is curved along circle 40, while hole 50 includes aposteriorly facing surface at least a portion of which is curved alongcircle 42 and an anteriorly facing surface at least a portion of whichis curved along circle 44. Additionally, as will be discussed more fullybelow in connection with the discussion of FIG. 11, the bone ispreferably prepared so that the anterior portion of the implant can befirst engaged with the prepared bone (FIG. 10A) and then the remainderof the implant can be pivoted into position so that first and secondpegs 26 and 28 are disposed within first and second holes 48 and 50,respectively (FIG. 10B) and the implant is ultimately snap or press fitonto the distal portion of the bone (FIG. 10C). As best shown in FIG.10C, holes 48 and 50 are sized to create an interference fit with pegs26, 28, respectively, so that the pegs are ultimately tightly fittherein. Of course, in other embodiments, the holes may be createdlarger than the pegs. It should be understood that although holes 28 and50 are shown and described as being formed in the bone, such structuresmay vary depending upon the particular configuration of the implants.

The aforementioned implantation of the implant with the distal portionof the femur is possible because of the relationship of pegs 26 and 28and the specially prepared femoral surface. In particular, holes 48 and50 are situated and similarly curved so as to receive the pegs when theimplant is pivoted about center point 46. As shown in FIG. 11, thedistal portion of the femur is also prepared so as to include a pivotsurface 52 that cooperates with the anterior of the implant. In thisregard, it is noted that the implant preferably includes a curvedanterior surface 54 to facilitate the pivoting. In other embodiments,the implant may include a separate structure, such as a bulbousextension that allows for the pivoting (shown in certain embodimentsdiscussed below). In still further embodiments, the implant may bepivoted about a virtual pivot rather than a specific structure. Aposterior portion of the femur is also preferably prepared to include atleast one divot 56 for accepting snap feature 30. This cooperation, asbest shown in FIG. 14, provides an additional fixation to the implantand bone construction. In the particular configuration shown in FIG. 11,a secondary divot 50 a is also created so as to allow an easy transitionof snap feature 30 into divot 56. The progression of snap feature 30into the two divots is best shown in FIGS. 12-14. Secondary divot 58essentially provides a first relief, thereby allowing snap feature 30 tosmoothly transition into divot 56. In other words, the cooperationoccurs in a stepwise fashion, which is important because either theimplant or the bone needs to deflect somewhat to allow for snap feature30 to become seated within divet 56. Secondary divet 58 provides forless deflection of both the bone and implant, which necessarily reducesthe possibility of implant deformation and/or fracture of the bone.

FIGS. 15 and 16 depict a similar progression of snap feature 30 intodivot 56, without the inclusion of a secondary divet 58. In theembodiment shown in those figures, the bone is prepared so that itincludes a tapered surface 60 that acts essentially as an infinitelystepped surface. Thus, divot 56 can move along surface 60 and into divot56 without requiring significant deformation of the implant and/orcausing fracture of the bone. Essentially, in both the embodiment shownin FIGS. 12-14 and the embodiment shown in FIGS. 15 and 16, a transitionis created to prevent the deformation of the implant and/or fracture ofthe bone. In other embodiments, such transition may take on variousgeometries.

FIGS. 17 and 18 illustrate alternate embodiments for the cooperationbetween the implant and the prepared distal portion of the femur. InFIG. 17, first peg 26 includes remains concentric with first hole 48, asin the embodiment shown in FIG. 9, but peg 28 is situated differently.Specifically, peg 26 includes an anteriorly facing surface and hole 48includes a posteriorly facing surface, both of which include portionsthat are curved along a first imaginary circle 38, and peg 26 includes aposterior facing surface and hole 48 includes an anteriorly facingsurface, both of which include portions that are curved along a secondimaginary circle 40. Both circles 38 and 40 are curved about centerpoint 46. Moreover, hole 50 includes a posteriorly facing surface atleast a portion of which is curved along a third imaginary circle 62 andan anteriorly facing surface at least a portion of which is curved alonga fourth imaginary circle 64. Again, both circles 62 and 64 are curvedabout center point 46. However, peg 28 includes an anteriorly facingsurface at least a portion of which is curved along a fifth imaginarycircle 61 and a posteriorly facing surface at least a portion of whichis curved along a sixth imaginary circle 63. Both circles 61 and 63 arecurved about a center point 65, which is different from center point 46.

On the other hand, FIG. 18 depicts a situation where the implant remainsin same form as it is shown in FIG. 9 (i.e., pegs 26 and 28 includesurfaces a portion of which are curved along concentric circles), butwhere hole 50 includes surfaces having a portion curved alongnon-concentric circles. Specifically, the relationship depicted in FIG.17 between peg 26 and hole 48 remains the same. Peg 28 includes ananteriorly facing surface a portion of which is curved along imaginarycircle 62 and a posteriorly facing surface a portion of which is curvedalong imaginary circle 64, where both of those circles are curved aboutcenter point 46. However, hole 50 includes a posteriorly facing surfacea portion of which is curved along imaginary circle 61 and an anteriorlyfacing surface a portion of which is curved along imaginary circle 63.Those circles 61, 63 are curved about center point 65, which isdifferent than center point 46.

In both FIGS. 17 and 18, the non-concentric relationship between peg 28and hole 50 creates an interference fit when the peg is ultimatelydisposed within the hole. FIGS. 19 and 20 depict the representativeprogression of implantation of an implant into a prepared bone inaccordance with that shown in FIGS. 17 and 18. While FIGS. 17 and 18depict two different manners in which the non-concentric relationshipcan be created to result in an interference fit, others exist. Forinstance, instead of an interference fit being formed between peg 28 andhole 50, an interference fit can be created between peg 26 and hole 48by varying their relationship in much of the same way as is describedabove in connect with FIGS. 17 and 18. In addition, it is contemplatedto create an implant and bone relationship where interference fits existbetween multiple pegs and multiple holes. For instance, both pegs 26 and28 may exhibit a non-concentric relationship with holes 48 and 50. Inother embodiments, implants having more than two pegs or other fixationmembers may likewise include multiple or only one non-concentricrelationship.

FIGS. 21-33 depict another embodiment according to the presentinvention, this embodiment pertaining to implants for use in replacing aproximal portion of the tibia. Specifically, tibial implants 112 and114, corresponding to the medial and lateral sides of the tibia,respectively, are shown and described in those figures. As best shown inthe exploded view of FIG. 22, medial implant 112 includes a medialbaseplate 116 and a medial insert 118, while lateral implant 114includes a lateral baseplate 120 and a lateral insert 122. In thepreferred embodiment, the base plates are constructed of a metallicmaterial, such as titanium, while the inserts are constructed of apolymer material, such as the crosslinked polyethylene offered under thename X3® by Stryker Corporation. Of course, other embodiments mayinclude base plates and inserts formed of various other materials, theonly limitation really being that such materials must be biologicallyacceptable. Likewise, although not focused upon in any of the figures,it should be understood that implants 112 and 114 employ structures forcausing their inserts to be fixed to their baseplates. These structurescan be any known or hereafter developed structures.

Turning now to FIGS. 23-27, the general design of certain of the commonfeatures between tibial implants 112 and 114 will be described in thecontext of a discussion of implant 112. It should be noted that incertain embodiments, the construction of these common features aresubstantially similar, but may vary in other embodiments. Moreover,other aspects of the tibial implants 112 and 114 may vary significantlyin order to ensure the cooperation of the particular implant with thedifferent anatomical features of the tibia. With a focus on medialtibial implant 112, it is shown that baseplate 116 has a bone facingsurface 124 that itself includes first and second pegs 126 and 128, adomed underside surface 130 (best shown in FIGS. 26 and 27), and a flatrun out 131 extending around domed surface 130. Referring back to FIG.22, it is noted that the proximal portion of the tibia is preferablyprepared in such fashion to receive pegs 126, 128, domed surface 130 andrun out 131. In this regard, the tibia is preferably prepared to includeholes 132, 146 and 134, 148 as well as a curved profile 136, 150,respectively. It should be understood that although both tibial implants112 and 114 are shown as having domed underside surfaces, theirrespective bone facing surfaces may simply be flat, or even of adifferent configuration, such as concave surfaces.

It should be understood that both implants 112, 114 are designed forimplantation on the proximal portion of the tibia in a similar fashionas are above-discussed femoral condyle implants 12, 14. With referenceto FIG. 28, implant 112 is shown, with a posteriorly and anteriorlyfacing surfaces of peg 126 being curved along imaginary concentriccircles 152 and 154, respectively, and posteriorly and anteriorly facingsurfaces of peg 128 being curved along imaginary concentric circles 156and 158, respectively. Those four circles are concentric about a centeror pivot point 160 that is located posterior to implant 112. Inaddition, pivot point 160 is in line with a plane 161 extending alongthe flat surface of run out 131. This is contrary to the depiction ofFIG. 29, where pivot point 160 is located posterior to implant 112, butoffset from the plane 161 along run out 131. Although both embodimentsoffer an implantation procedure similar to the above-discussed femoralimplants, it should be noted that the offset nature of the pivot pointin FIG. 29 may allow for ease of insertion of a component in a smallworking volume. For instance, offsetting the pivot point may allow foreasier insertion of the implant into small spaces, which is important incertain surgical techniques such as minimally invasive techniques. Itshould be understood that this concept may be employed in any of theimplant designs discussed herein.

FIGS. 30-36 depict a bi-cruciate retaining (“BCR”) tibial implant foruse in surgeries where the anterior and posterior cruciate ligaments arespared, or a suitable synthetic ligament is employed. BCR implant 210includes tibial components 212 and 214, which are attached via abridging component 216. Both components 212 and 214 include a base plateportion (which are the portions connected together via bridging portion216) and insert portions, in similar fashion as above-discussed tibialimplants 112, 114. The base plate of component 212 includes a bonefacing surface 218, which in turns includes a peg 220, a domed surface222 and flat run out 223. Likewise, component 214 includes a bone facingsurface 224 that in turns includes a peg 226, a domed surface 228 and aflat run out 229. As in the above-discussed tibial implants, flat runouts 223 and 229 surround domed surfaces 222 and 228, respectively.

Turning to FIG. 32, it is shown that implant 210 exhibits a similarconstruction to the above-discussed femoral and tibial implants in thatpegs 220 and 226 (only component 212 is shown in the figure) includes aposterior facing surface curved along a circle 230 and an anteriorfacing surface curved along a circle 232. Those circles are concentricabout a pivot point 234, which is situated posterior of the implant butalong a plane 236 extending along run out 223. Thus, implant 210 may beimplanted in a similar fashion as in the above-discussed implants.Likewise, implant 210 can exhibit any of the modifications discussedabove in connection with the femoral and tibial implants. For instance,pivot point 234 could both be located posteriorly and offset from plane236, as in the above-discussed tibia implant depicted in FIG. 29.Moreover, it should be understood that the tibia can be prepared toreceive implant 210 in a similar fashion as it is in connection with theabove-discussed tibia implants.

FIGS. 33-36 depict a variation of implant 210 where an anterior keel 238is provided on bridging component 216. As shown in FIG. 36, thiscomponent includes a posterior facing surface defined by a circle 240and an anterior facing surface defined by an imaginary circle 242, thosecircles being concentric about pivot point 234 along with circles 230and 232 defined by peg 220. Effectively, anterior keel 238 acts in asimilar fashion as do the second pegs discussed above in connection withthe femoral and tibial components. With specific reference to FIG. 35,it is shown that keel 238 is shallower toward its center to avoiddisruption of an eminence of the proximal portion of the tibia. Thisconstruction requires less of the eminence to be resected to receivekeel 238, which in turn, lessens the chance of the anterior cruciateligament pulling away from the eminence or the eminence fracturing underthe pressure created by the pulling force created by the anteriorcruciate ligament.

Although certain embodiment BCR implants are shown and described herein,other BCR implant designs may be employed in accordance with the presentinvention. For instance, while maintaining the structures facilitatingthe implant-bone connection, BCR implants could retain other structuressuch as are taught in U.S. patent application Ser. No. 12/987,380, thedisclosure of which is hereby incorporated by reference herein.

FIG. 37 depicts a patello-femoral implant 310. FIGS. 37-39 illustratedifferent perspective views of one embodiment of a patello-femoralprosthetic implant 310. Like the above-discussed implants, implant 310may be manufactured from cobalt chrome, titanium, polyethylene, PEEK orother known implantable materials. Implant 310 includes an articularsurface 311, a bone contacting surface 312, an anterior end 313 and aposterior end 314. The articular surface may be equivalent to thatdescribed in U.S. Patent Application 2010/0222781, the disclosure ofwhich is hereby incorporated by reference in its entirety. Implant 310further includes a primary peg 320 and a fixation feature 330. Onceimplanted, articular surface 311 of implant 310 is designed to replacethe diseased articular cartilage of the trochlear groove of thepatella-femoral joint, and will function by articulating with either anative or prosthetic patella implant.

Bone contacting surface 312 is designed to interface with the resectedregion of the trochlear groove. As with the above-discussed implants,the resected region of the cartilage and bone may be of planar ornon-planar geometry.

Primary peg 320 is comprised of a primary peg radius 321 that has aprimary peg center 322. The primary peg may have an elongate structurewhich extends from the bone contacting surface, as shown in the currentembodiment. Further, the elongate structure may be straight, angled orcurved with respect to the anterior end of the implant. In an alternateembodiment, primary peg 320 and the associated radius 321 and center 322geometries may be built into the peripheral rim of the implant. In stillfurther embodiments, there may not be a physical primary peg structure,but rather a theoretical primary peg center 322 which will serve as ageometric reference for various implant fixation features which aredescribed herein. A physical or theoretical primary peg center may belocated on any region of the implant including, but not limited to theanterior end, posterior end, medial end, and lateral end.

Fixation feature 330 is an elongate member extending from the bonecontacting surface 312. In the embodiment shown, feature 330 is a bonepeg including an anterior surface 331 and a posterior surface 332, bothextending from bone contacting surface 312. Anterior surface 331 has ananterior surface radius RA, forming a concentric geometry about theprimary peg center 322. In the embodiment shown, posterior surface 332has a posterior surface radius 333 which is not concentric about primarypeg center 322. In alternate embodiments, posterior surface 332 may beconcentric about primary peg center 322.

It should be noted that any concentric geometric regions of eitheranterior surface 331 or posterior surface 332 may occupy a portion ofthe respective surfaces. For example, in one embodiment the concentricgeometry on anterior surface 331 may cover approximately 50 percent ofanterior surface 331 as seen from a side view perspective. In analternate embodiment, approximately 100 percent of anterior surface 331may be covered by a concentric geometry as seen from a side viewperspective. The coverage may range from 25 percent to 100 percent ofcoverage of any concentric or non-concentric geometries.

FIGS. 40a-40d are a series of cross-sectional views illustrating themethod of implantation for patello-femoral implant 10. Step 1 (FIG. 40a) of this method involves preparation of the distal femur 1. In thisembodiment, the prepared boned surface is a non-planar resected bonesurface 340, a resected region for receiving the primary peg 341 and aresected region for receiving fixation feature 342. In step 2 (FIG. 40b), primary peg radius 321 contacts the posterior aspect of the resectedbone for receiving the primary peg 320. In step 3 (FIG. 40c ), theimplant is rotated about the primary peg radius 321 until fixationfeature 330 enters the resected region for receiving fixation feature342. Step 4 (FIG. 40d ) illustrates a view of the implant 10 fullyimplanted.

During this method of implantation, an implantation path 350 is formedby following the primary peg center 322. Path 350 is a primary approachpath until final seating which occurs when path 350 is substantially acurved path. The approach path may follow various paths, an example ofwhich is a linear path. When an implantation path 350 is predetermined,the primary peg center 322 remains coincident with the implantationpath. While peg center 322 progresses about the implantation path, theimplant may rotate, thus the fixation feature 330, with concentricgeometries by rotating about a path concentric to peg center 322. Whenin the final position, there is an over resected bone region 343 at theposterior aspect of primary peg 320. Further, the design of the anteriorsurface radius RA and posterior surface radius 333 allows forimplantation of fixation feature 330 without the need for boneover-resection in this region. This is noted because when the knee movesthrough a range of motion the patella (either native or prosthetic) willtransfer the variable and increasing loads through the implant 10. Giventhat the over resected bone region 343 is located on the posterioraspect of the primary peg 320, load will be transferred directly to thebone. Thus, this implant design will remain locked in place and minimizethe risk of implant loosening.

Further regarding the implantation path 350, this unique path 350geometry allows for positive seating of the implant into its properposition and results in an optimized final position of peg 320 andfixation feature 330. Implantation path 350 is substantially linear asthe implant approaches the prepared bone. Path 350 then becomessubstantially curved as the implant is finally seated and thereforelocked into position. Alternately stated, the implant travels along apath 350 where the primary peg center 322, physical or theoretical, ispreferably coincident with the implantation path. The orientation of theimplant to the path is maintained throughout, such that the implant mayrotate about the peg center 322 when traveling about a substantiallycurved, or linear, section of the implantation path. This rotation formsa concentric arcuate pathway of implantation.

FIGS. 41 and 42 illustrate another embodiment of a patello-femoralprosthetic implant 410. Implant 410 includes an articular surface 411, abone contacting surface 412, an anterior end 413 and a posterior end414. Implant 410 further includes a primary peg 420, fixation features430 a and 430 b and elements 460 a and 460 b. Primary peg 420 has aprimary peg radius 421 and center 422. In this embodiment, the peg 420is built into the periphery of the anterior end 413 of the implant 410.Fixation features 430 a and 430 b have respective anterior surfaces, 431a and 431 b, and posterior surfaces, 432 a and 432 b. Surfaces 431 a,431 b, 432 a and 432 b are designed with concentric radii (RA, RB, RCand RD) about the primary peg center 422.

Elements 460 a and 460 b are protrusions from bone contacting surface412. The function of these elements is to provide additional fixation,strength and/or stability to implant 410. In this embodiment eachelement 460 has a radius of curvature, RH. RH may be different for eachelement, 460 a and 460 b. Further, RH has no relation to concentricradii: RA, RB, RC and RD.

The method of implantation of implant 410 is consistent with thatpreviously described for implant 10. The primary peg center 422 remainscoincident about an implantation path and implant 410 may rotate aboutprimary peg center 422. An aspect of differentiation is that bone mayneed to be over resected along the posterior aspect of each fixationfeature, 430 a and 430 b, because of the concentration radii relation tothe peg center 422 on their respective posterior surfaces, 432 a and 432b.

Other embodiment patello-femoral implants are envisioned, in which therewill be at least one fixation feature, but there also may be a pluralityof fixation features. These features will each have an anterior surfaceand a posterior surface with a relation to a primary peg center.Similarly, there may be none, one or a plurality of elements to provideadditional stability. Still further, the peg geometries may includethose as described in U.S. Pat. No. 7,294,149, the disclosure of whichis hereby incorporated by reference in its entirety. Further, peg shapesmay be cylindrical, hexagonal, cruciform, square, or other suchgeometries. The method of implantation will be consistent with themethods previously described where the primary peg center follows andremains coincident along an implantation path and the implant may rotateabout the primary peg center, then locking into its final position.

Another embodiment femoral implant 510 similar to above-discussedimplants 12 and 14 is depicted in FIGS. 43-45. The particular implantshown in those figures is designed as a unicondylar knee replacement(“UKR”) for a unicondylar knee arthroplasty procedure. However, likeimplants 12 and 14, implant 510 may be utilized in a system such as isshown in FIG. 1. In the embodiment shown, the articular surface ofimplant 510 may have a sagittal geometry similar to that described inU.S. Pat. No. 5,824,100, the disclosure of which is hereby incorporatedby reference in its entirety. Once implanted, unicondylar implant 510will articulate with a prosthetic tibial implant.

FIG. 44 depicts unicondylar implant 510, which includes an articularsurface 511, a bone contacting surface 512, an anterior end 513 and aposterior end 514. FIG. 45 is a side view of implant 510, where primarypeg 520 and a fixation feature 530 can be seen. Peg 520 has a primarypeg radius 521 and a primary peg center 522. Fixation feature 530includes an anterior surface 531 and posterior surface 532 extendingfrom the bone contacting surface 512. Further, anterior surface 531 hasa radius RB and posterior surface 532 has a radius RC. Radii RB and RCare concentric about primary peg center 522. As previously described,concentric Radii RB and RC on respective surfaces 531 and 532, may coverbetween the range of 25 to 100 percent of the surface as seen from aside view perspective. Of course, it is contemplated that Radii RB andRC may cover less than 25 percent of the surface. Further, theconcentric coverage on anterior surface 531 may be the same as, ordifferent than, the concentric coverage on posterior surface 532.

FIGS. 46a-46c illustrate a method of implantation for implant 510.Similar to the methods described above, primary peg center 522 iscoincident along an implantation path 550. Implant 510 is rotated aboutcenter 522, while moving about implantation path 550 and into a finallocked position. In this embodiment, the path may be substantiallycurved, and may or may not have a linear aspect. What is differentiatedabout this specific method is the specific location of the over resectedbone regions, 543 a and 543 b. Region 543 a is located on the anterioraspect of the bone contacting surface 512 of the poster condyle. Region543 b is located on the posterior aspect of the posterior surface 532 ofthe fixation feature 530.

FIGS. 47 and 48 are perspective views of another embodiment of aunicondylar implant 610, which includes an articular surface 611, a bonecontacting surface 612, an anterior end 613 and a posterior end 614.Here, two peg features 615 and 616 may each have a similar configurationand size diameter for the length of the peg. In particular, peg features615 and 616 exhibit a rounded rectangular shape. Alternately, theconfiguration of peg features 615 and 616 may be different, constant,tapered, or any combination thereof. For instance, in other embodiments,the peg features may be cylindrical with constant or non-constantdiameters.

As best shown in FIG. 48 implant 610 further includes a primary peg 620and fixation features, 630 a and 630 b. Primary peg 620 includes aprimary peg radius 621 and a primary peg center 622. Fixation features,630 a and 630 b, each comprise respective anterior surfaces, 631 a and631 b, and posterior surfaces, 632 a and 632 b, which extend from thebone contacting surface 612. Surfaces 631 a, 632 a, 631 b and 632 b haveradii RA, RB, RC and RD which are concentric about peg center 622. Aspreviously mentioned, the percent surface area concentric geometrycoverage may range from 25 to 100 percent of the respective anterior andposterior surfaces as seen from the side view. In one embodiment, thepercentage of concentric geometry coverage may be the same for allsurfaces of all pegs. In an alternate embodiment, the percentage ofconcentric geometry coverage may be different for all surfaces of allpegs. It is understood that there can be any combination of percentageof concentric geometry coverage on any respective surface and for on anyrespective peg feature.

Angled line 650 shows the relationship between primary peg 620 andfixation features 630 a and 630 b. Line 650, as illustrated, is astraight line between a tangent point of primary peg radius 621 and atangent point on the distal most tip of feature 630 b. In the embodimentshown, the length of 630 a extends beyond line 650. In otherembodiments, a primary peg 620 and all fixation features, 630 a and 630b, would extend to a length ending on angled line 650. Further, asmoving away from a physical or theoretical center point, one, two ormore fixation features may increase in size. In yet other embodiments,fixation feature 630 a may not extend to angled line 650. Thisrelationship of fixation features may further include posterior end 614,where end 614 may extend beyond, to or below line 650. In yet otherembodiments of angled line 650, the origin of the feature may bereferenced from center 622 instead of a tangent point.

In another embodiment of line 650, it may be formed by connection toeither a center point (not show) of a distal radius of a fixationfeature or a tangent point of a fixation feature. This angled linerelationship may be included in all embodiments of the contemplatedinventions and is important to the function of the implant because thisrelationship of peg and feature length will dictate when the preparedbone is contacted by the implant during implantation. Methods ofimplantation for implant 610 are consistent with those previouslydescribed.

FIGS. 49-52 depict another embodiment unicondylar implant 710 and anassociated interface within a distal femoral bone 701. Implant 710includes an articular surface 711, a bone contacting surface 712, ananterior end 713 and a posterior end 714. Implant 710 preferably has aprimary peg 720 having a primary peg radius 721 and a primary peg center722. Implant 710 preferably further includes a first fixation feature730, a second fixation feature 731 and a third fixation feature 732,each extending from bone contacting surface 712. First fixation feature730 has an anterior surface 733 and a posterior surface 734, whereinanterior surface 733 follows a radius RD and posterior surface 734follows a radius RE. Radii RD and RE are concentric about peg center721.

Second fixation feature 731 and third fixation feature 732 are bothoffset posteriorly with respect to first fixation feature 730. Further,fixation features 731 and 732 are offset in respective medial andlateral regions of the implant with respect to first fixation feature731. In the embodiment shown, fixation features 731 and 732 are spacedequally in the respective medial and lateral directions. In alternateembodiments, the offset spacing may be different with respect to any of,or any combination of the posterior, medial and lateral directions.

Second fixation feature 731 and third fixation feature 732 furtherinclude respective anterior surfaces 735 and 736, and respectiveposterior surfaces 737 and 738. Posterior surface 738 of third fixationfeature 732 is not shown. In the embodiment shown, anterior surfaces 735and 736, and posterior surfaces 737 and 738 include a geometry that isconcentric about the primary peg center 721. However, in alternateembodiments, any one of, or combination of surfaces 735, 736, 737 or 738may include geometry concentric about primary peg 721. Yet otheralternate embodiments of fixation features 730, 731 or 732 may includeany of the geometric relationships previously described.

Further, implant 710 includes a posterior locking feature 740. Posteriorlocking feature 740 extends from bone contacting surface 712 and has afirst width W1 and a second width W2. In the embodiment of feature 710shown, the profile is a substantially curved extrusion with second widthW2 being greater than first width W1. In alternated embodiments, widthW2 may be substantially equal to width W1. In yet other embodiments,there may be multiple posterior locking features spaced located on theposterior aspect of the implant.

In the embodiment shown, bone contacting surface 712 includes a curvedregion 745 and a flat region 746. Curved region 712 extends from theanterior end 713 and includes fixation features 730, 731 and 732. Flatregion 746 extends from posterior end 714 and includes posterior lockingfeature 740. Further, curved region 745 comprises a significant portionof bone contacting surface 712 compared to flat region 746. Specificallyregarding this embodiment, bone contacting surface 712 is comprised ofapproximately 75 percent curved region 745 and 25 percent flat region746. In alternate embodiments, the area of surface 712 may be comprisedof different percentage ratios of curved region 745 to flat region 746.For example, in an alternate embodiment, the area coverage of surface712 may be comprised of approximately 50 percent curved region 745,compared to 50 percent flat region 746. In other embodiments, posteriorlocking feature 740 may extend from a curved region 745 of bonecontacting surface 712.

Multiple cross-sections are shown to illustrate the final position ofimplant 710 onto bone 701. Referring to FIG. 51, a cross-sectional viewthrough the first fixation feature 730 is shown. In the “Detail A” view,an interference region 750, clearance region 751 and contact region 752are shown. Here, clearance region 751 is centrally located on theposterior surface 734 as shown in this side view. Further, the clearanceregion 751 comprises approximately 50 percent of posterior surface 734.In alternate embodiments, the clearance region may comprise between arange from 25 to 75 percent of the posterior surface. In all cases,clearance region 751 is preferably surrounded by contact regions asshown in the sagittal view. Interference region 750 is substantiallycentrally located on anterior surface 733 and is surrounded by contactregions as shown in FIG. 51. A resultant force L1 creates a biasedpress-fit at the implant-bone interface.

Referring to FIG. 51, a cross-sectional view through the first fixationfeature 731 is shown. In the “Detail B” view, an interference region755, clearance region 754 and contact region 756 are shown. Interferenceregion 755 is shown in a approximately centrally located position onposterior surface 737 of fixation feature 731 and has an associatedresultant force of L2 which creates a biased press-fit at theimplant-bone interface. Here, interference region 755 approximatelycovers 50 percent of posterior surface 737, but may cover between 25 to75 percent of posterior surface 737 in alternate embodiments.Interference region 755 is adjacent to clearance region 754 in onedirection and is adjacent to contact region 756 in an oppositedirection. As shown, contact region 756 continues about the anteriorsurface 735. In alternate embodiments, interference region 755 may besurrounded by contact regions. Although not shown, the cross-sectionalview through fixation feature 732 is similar to that just described andhas a resultant force of L3 (not shown) at an interference region.

With respect to the cumulative effect of the resultant forces L1, L2 andL3, force L1 acts on anterior surface 733 while forces L2 and L3 act onthe respective posterior surfaces 737 and 738. Alternately stated, forceL1 acts in an equal and opposite direction to the combination ofresulting forces L2 and L3. The result of this biased press-fit loadingpattern is a benefit in the initial fixation at the implant-boneinterface. Here, the unique implant geometries and bone preparationenable the implant to essentially be held or gripped in place under thepress-fit loading created by the sum of the resulting forces.

While the implantation of implant 710 onto prepared bone 701 is notshown, it would follow the implantation path philosophy previouslydescribed. Here, the physical peg center 722 is coincident along animplantation path. The implantation path may have linear and arcuateshapes. During implantation, peg center 722 remains coincident along thepath while the implant rotates, thus rotating fixation features 730, 731and 732 along the concentric arcs which are concentric about peg center722. As the implant nears the end of the implantation path and the finalseating is about to occur, peg center 722 translates, thus incorporatinga cam like locking/interference of the first fixation feature 730 withbone 701. The fixation of feature 730 with bone 701 essentially createsa primary locking resultant force as represented by L1. As features 731and 32 are seated into final position, a set of secondary lockingresultant forces are established which are represented by L2 and L3.Force L1 may act in opposition to forces L2 and L3 to lock the implantto the bone and provide and enhanced initial fixation.

It should be noted that the resultant forces generated by aninterference between the implant and bone may be achieved in variousways. The forces may be the result fully of the implant preparation,fully within the implant design, or a combination of the implantpreparation and implant design. In any scenario, the a physical ortheoretical center point would be coincident with an implantation path,the implant may simultaneously rotate about the center point and thefinal seating of the implant would have a plurality of resultant forcesdesigned to enhance the initial fixation of the implant by locking itonto the bone.

FIGS. 53-56 depict yet another embodiment unicondylar implant 810 andassociated interface within a distal femoral bone 801. Implant 810 has aprimary peg 820 having a primary peg radius 821 and primary peg center822. Implant 810 has three fixation features 830, 831 and 832. Features831 and 832 have respective posterior surfaces 837 and 838 as shown. Akey difference between implant 810 and those previously described, forinstance, implant 710 (shown in FIGS. 49-52), is that posterior surface737 is concentric about peg center 722, whereas posterior surface 837 isnot concentric about peg center 822.

In FIG. 55, both illustrations marked “Detail C” are similar to thoseillustrations marked with “Detail A” previously described in FIG. 51.However, there are differences between illustrations marked “Detail D”in FIG. 56 and illustrations marked “Detail B” in FIG. 52. Regarding“Detail D,” there is an interference region 855, which is surrounded bycontact regions 856. Interference region 855 approximately covers 75percent of posterior surface 837. Therefore, the geometry of theposterior surface 837 enables unique bone preparation and implant-boneinterface contact. In contrast, “Detail B” in FIG. 52 includesinterference region 755 surrounded by both a clearance region 754 andcontact region 756. Further, region 755 covers approximately 50 percentof posterior surface 737.

FIGS. 57-59 depict another unicondylar implant 910 and associatedinterface with a distal femoral bone 901. Implant 910 is similar to, andincludes all features previously described with respect to implant 510.In contrast to implant 510, implant 910 contains both a flat bonecontacting region 966 and a curved bone contacting region 945. Flatregion 966 may enable easier preparation of the posterior distal femoralbone. Implant 910 also includes a posterior locking feature 940 locatedwithin flat region 966 and having a curved profile 941. Feature 940 is alocking feature that engages the bone late during implantation andprovides additional stability. Profile 941 is designed with a geometryequivalent to that of a rotational preparation tool such as a burr.Feature 940 may have all of the features described with respect toposterior locking feature 740.

FIGS. 60-63 depict a tibial implant 1010 and associated interface withina proximal tibial bone 1001. Implant 1010 may be monolithic and made ofpolyethylene or other suitable material as shown, or it alternately maybe a modular design including a polymeric insert component and a metaltray component. Implant 1010 preferably has a bearing surface 1011, abone contacting surface 1012, an anterior end 1013, a posterior end1014, an inner side 1015 and an outer side 1016. Bearing surface 1011preferably has profile designed to articulate with an articular surfaceof a femoral prosthetic implant, such as a unicondylar implant aspreviously described. In the embodiment shown, implant 1010 contacts thebone on surface 1012, inner side 1015 and outer side 1016. Inner side1015 may be substantially perpendicular to bone contacting surface 1012as shown, or side 1015 may alternately have an angular relationship withsurface 1012. Outer side 1016 contacts a small portion of proximaltibial bone 1002. In alternate embodiments, proximal tibial bone 1002may be resected and therefore outer side 1016 would not be contactingbone.

Referring specifically to FIG. 63, an elongate element 1020 preferablyextends from bone contacting surface 1012 of implant 1010. As shown inthis cross-sectional view, peg 1020 has a first side 1021, a second side1022 and a distal end 1023. Element 1020 may have a generallycylindrical, hexagonal, or other geometric shape, including the peggeometries previously disclosed. Further, distal end 1023 may have manydifferent geometries such as rounded (as shown), spiked, flared, taperedor other ending geometries. Further, a first interference region 1030 isshown and defined as the interface between inner side 1015 and an innerwall of bone 1001. First interference region 1030 has a resultantpress-fit force of L11. A second interference region 1035 is shown anddefined as the interface between second side 1022 and bone 1001. Secondinterference region 1035 has a resultant press-fit force of L12. Duringimplantation of implant 1010 onto bone 1001, the second interferenceregion 1030 drives the component toward the inner side thus creating thefirst interference region 1030. The resultant forces act to seat theimplant in the appropriate medial/lateral location and further toprovide improved initial fixation of the implant onto the bone. Itshould be noted that resultant forces L11 and L12 are offset from eachother as shown.

FIG. 64 is a cross-sectional view of the tibial implant shown in FIGS.60-63 further compromising geometric relationships between the implantand the bone. Element 1020 has an element central axis 1038 and areference point 1040 a on inner side 1015. Element 1020 has a width “d”and the distance from axis 1038 to reference point 1040 a is “a”.Prepared bone 1001 has cavity 1050 prepared for receiving peg 1020.Cavity 1050 has a cavity central axis 1037. Bone 1001 has a referencepoint 1040 b which, when implant 1010 is fully seated will contact point1040 a. Cavity 1050 has a width of “d-x” and the distance from axis 1037to point 1040 b is “a-y”. During implantation there is a press-fit ofpeg 1020 into cavity 1050. As point 1040 a seats upon point 1040 b, thedifference between “a” and “a-y” and/or “d” and “d-x” results in aninterference which biases the implant such that central axis 1038 isoffset from axis 1037. This geometric relationship causes the respectiveinterference loads and resultant forces previously described in FIG. 63.

FIGS. 65-67 depict yet another embodiment patello-femoral prostheticimplant 10. FIG. 1 illustrates patello-femoral implant 10 in animplanted state, where it will articulate with either a native orprosthetic patella. Among the differences between implant 10 and, forinstance, implant 310, is the inclusion of two pegs in place of fixationfeature 330. However, implant 10 is largely implanted in the samefashion as the other patella-femoral prosethic implants discussedherein.

Although several of the embodiment implants discussed above are designedfor engagement with prepared bone surfaces that do not exhibit planarsurfaces, it should be understood that the implants could be modified toalso engage with such planar surfaces. Moreover, although one method forpreparing the bone surfaces to receive the implants of the presentapplication could be the use of a milling instrument or the like(including a milling instrument coupled with a robot or the like), othermethods may be utilized. For instance, reamers, saw blades, or othercutting instruments may be adapted to be utilized in the implantationprocedures for the present implants.

Overall, the various invention embodiments described herein utilize aplurality of or at least one concentric shaped feature (fins, keels,pegs) having a specific relationship to a prepared bone. Therelationships of the implant and bone contacting surface may be aninterference fit, clearance or interference relationship. Further, thisrelationship serves to fixate, or lock, the implant to the prepared bonesurfaces. Alternately stated, the locking resultant forces generated atthe interference regions of the implant and bone, establish an enhancedinitial fixation of the implant. The enhanced fixation is critical,especially in the zero to six month post-operative period when boneongrowth and/or ingrowth occurs.

Moreover, as noted above, the various implants described above may bedesigned for a cemented application, and in such case, their respectivebone facing surfaces may be finished with a treatment, such as gritblasting, which will optimize the mechanical attachment to bone cementor other known attachment materials such as bone adhesives. An exampleof a medical adhesive is described in U.S. Patent Application Nos.2009/0318584, 2009/0280179, and 2010/0121459, the disclosure of whichare all hereby incorporated by reference in their entirety. Incementless applications, the bone contacting surfaces of the variousimplants may be treated with bone growth agents such as peri-apetite orhydroxy-apetite. Further, the bone contacting surface may have aningrowth structure such as beads or a porous metal structure. An exampleof a beaded ingrowth structure is described in U.S. Pat. No. 4,550,448,the disclosure of which is hereby incorporated by reference in itsentirety. The porous metal structure may be manufactured from thetechnology described in U.S. Pat. Nos. 7,537,664, 7,674,426, and7,458,991, and U.S. Patent Application Nos. 2006/0147332 and2006/0228247, the disclosures of which are all hereby incorporated byreference in their entireties. It is understood that all embodiments ofthe inventions described herein may utilize any combination of bonegrowth agents or structures to promote initial fixation and subsequentbone ongrowth and/or ingrowth.

Likewise, the various implants discussed herein may be formed of anysuitable material for use in human implantation. For instance,embodiments are described above as being formed of metallic or polymericmaterial. However, the specific materials noted above should not beconsidered exhaustive of those that can be utilized. Indeed, othersuitable materials may be employed in connection with the variousimplants. For instance, in embodiments where a polymeric material isidentified, other suitable polymeric materials may be substituted. It iscontemplated to utilize the materials and material combinations taughtin U.S. Patent Application Publication No. 2010/0312348, the disclosureof which is hereby incorporated by reference herein.

Although described for specific uses above, the inventions describedherein may used in other knee implant prosthesis designs including:focal defect repairs, bicondylar, bi-cruciate retaining, total kneereplacements, revision knee replacements or hinged knee replacements.The inventions may also be used in any large or small articulatingjoints with the body including but not limited to: hip, shoulder, knee,hand, wrist, ankle or vertebral. Regarding spinal applications, thistechnology may be applied to vertebral body replacement devices,interbody spacers or articulating prostheses for any region of the spineincluding: lumbar, thoracic or cervical. This technology may further beapplied in trauma or craniomaxillofacial applications.

Various embodiments of inventions have been described herein and it isunderstood that any of the features, or any combinations of any of thefeatures, may be used in any alternate embodiments of a prostheticimplant. For example, any embodiment of a patello-femoral or unicondylarimplant described herein may utilize a theoretical peg center as ageometric reference as opposed to a physical primary peg feature, whichcontains a primary peg center. Moreover, although certain specificstructural aspects of certain preferred embodiments are shown anddiscussed herein, those preferred embodiments may vary while remainingsquarely within the purview of the present invention. For instance,certain embodiment implants are shown as having specifically shapedfixation elements (e.g., cylindrical pegs). However, those elements maybe modified according to the present invention (e.g., cylindrical pegsmay be modified so as to be differently shaped pegs, keels can besubstituted for the cylindrical pegs, etc. . . . ).

In addition, as mentioned above, the various prepared bone surfacesdescribed herein may be formed through the use of many different means.For instance, traditional cutting or milling operations may be employed,as can the use of a cutting or milling instrument coupled with a robotor the like. Suitable robots may include the robotic systems describedin U.S. Pat. Nos. 6,676,669; 7,892,243; 6,702,805; 6,723,106; 6,322,567;7,035,716; 6,757,582; 7,831,292; 8,004,229; 8,010,180; 6,204,620;6,313,595; and 6,612,449; U.S. Patent Application Nos. 2010/0268249;2008/0202274; 2010/0268250; 2010/0275718; 2003/0005786; and U.S.Provisional Application No. 61/530,614 filed Nov. 16, 2011, thedisclosures of which are hereby incorporated by reference herein.Likewise, such robots or similar robots may be utilized in placing anyof the above-discussed implants on the bone. In either case, particularrobotic system employed may include the use of a surgical system, suchas is disclosed in U.S. Pat. No. 7,725,162 (“the '162 patent”), thedisclosure of which is hereby incorporated by reference herein. Inparticular, the '162 patent discloses a navigation system that may beutilized in guiding a robotic system with respect to a bone or otheranatomical structure.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. (canceled)
 2. A method of arthroplasty comprising: creating aresected bone surface of a bone; preparing a first cavity extending intothe resected bone surface, the first cavity having an arcuatelongitudinal curvature; providing a prosthetic implant having anarticular surface, a bone contacting surface, and a first peg extendingfrom the bone contacting surface, the first peg having an arcuatelongitudinal curvature; contacting the resected bone surface with apivot surface of the prosthetic implant; and coupling the prostheticimplant to the bone by pivoting the prosthetic implant about the pivotsurface while the pivot surface remains in contact with the resectedbone surface such that the first peg enters the first cavity.
 3. Themethod of claim 2, wherein the creating step includes utilizing acutting tool coupled with a robot.
 4. The method of claim 2, furthercomprising preparing a second cavity in the resected bone surface. 5.The method of claim 4, wherein the step of contacting the resected bonesurface with the pivot surface of the prosthetic implant includesinserting an end of the prosthetic implant that includes the pivotsurface into the second cavity.
 6. The method of claim 4, wherein thepreparing step further includes preparing a third cavity extending intothe resected bone surface.
 7. The method of claim 6, wherein the implantincludes a second peg extending from the concave portion of the bonecontacting surface and having a second curved surface, the second curvedsurface concentrically curved with the first curved surface about apoint on the pivot surface, and the implanting step includes disposingthe second curved surface within the third cavity.
 8. The method ofclaim 6, wherein the implant includes a second peg extending from theconcave portion of the bone contacting surface and having a secondcurved surface, the second curved surface of the second peg and thefirst curved surface of the first peg being non-concentrically curvedwith respect to one another, and the implanting step includes disposingthe second curved surface within the third cavity.
 9. The method ofclaim 2, wherein the first peg includes a second curved surface.
 10. Themethod of claim 9, wherein the preparing step includes preparing thefirst cavity to include a third curved surface corresponding to thefirst curved surface of the first peg and a fourth curved surfacecorresponding to the second curved surface of the first peg.
 11. Themethod of claim 10, wherein the first, second, third, and fourthsurfaces are concentric with respect to one another after the implant iscoupled to the bone.
 12. The method of claim 10, wherein after the stepof positioning the pivot surface of the prosthetic implant in contactwith the bone and before the step of coupling the implant to the bone,the first and second surfaces are curved about a first point and thethird and fourth surfaces are curved about a second point, the first andsecond points being different.
 13. The method of claim 2, wherein theimplant further includes a first projection.
 14. The method of claim 13,further comprising the step of creating a first divot in the bone. 15.The method of claim 14, wherein the implanting step includes disposingthe first projection within the first divot.
 16. The method of claim 15,further comprising the step of creating a second divot in the bone andwherein the implanting step includes disposing the first projectionwithin the second divot.
 17. The method of claim 16, wherein the firstprojection is first positioned in within the first divot, and then thefirst projection is next positioned within the second divot.
 18. Themethod of claim 13, wherein the first projection is ball shaped.
 19. Themethod of claim 2, wherein the bone contacting surface includes a flatportion defining a first plane, the pivot surface located on the firstplane.
 20. The method of claim 2, wherein the implanting step isperformed through the use of a robot.